Justification This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Family/Sub-family Laridae

Species name author (Linnaeus, 1758)

Taxonomic source(s) AERC TAC (2003), AOU checklist (1998 + supplements), Christidis and Boles (1994), Christidis and Boles (2008), Cramp and Simmons (1977-1994), Dowsett and Forbes-Watson (1993), SACC (2005 + updates), Sibley and Monroe (1990, 1993), Stotz et al. (1996)

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

650,000 - 1,800,000

unset

-

No

Range & population The Black Tern is found in the Old and New World. It ranges from southern Scandinavia to southern Spain, east through Europe and western Asia to central Mongolia. Individuals from this area predominately winter on the Atlantic coast of Africa, from the Western Sahara to South Africa. It is also found across much of Canada to northern regions of the USA, with individuals wintering on the Pacific coast of Mexico, the Pacific and Atalantic coast of Central America and northern South America¹.

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: Behaviour This species is strongly migratory¹ and travels both over land and over sea⁴. It breeds between May and June¹ in colonies, usually of less than 20 pairs (rarely more than 100 pairs)¹ and often close to other species^{3, 4}. After breeding it departs for its wintering grounds from July onwards², returning north again from late-March⁴. The species is gregarious throughout the year⁴, foraging in groups of 2-20 during the breeding season and congregating in large flocks offshore on passage and in the winter over shoals of predatory fish^{1, 2, 4}. Habitat Breeding The species breeds on fresh or brackish wetlands² such as small pools, lakes, marshes^{1, 2}, ditches, overgrown canals, quiet reaches of rivers, swampy meadows², peat bogs and rice-fields¹, showing a preference for well-vegetated areas¹ with sparse, open emergent vegetation¹ (e.g. Typha spp., sedge or reeds)³ and floating water-lilies¹, and with water 1-2 m deep¹. It generally avoids small marshland areas less than 4 ha in area¹. Non-breeding On passage the species frequents inland wetlands including pools, ditches¹, reservoirs, lakes and sewage farms⁴, as well as coastal habitats and estuaries¹. In winter it is predominantly coastal however, frequenting estuaries^{1, 4}, saltmarshes, bays⁴, coastlines and coastal lagoons¹ as well as marine waters up to 400-600 km offshore⁵. Diet Breeding Its breeding diet consists predominantly of insects (e.g. chironomids, Odonata, Ephemeroptera and Coleoptera) as well as small fish¹ and amphibians⁴ (e.g. tadpoles and frogs)¹. Non-breeding On passage and during the winter the species's diet consists largely of marine fish although insects and crustaceans may also be taken⁴. Breeding site The nest may be a low compressed mound of plant matter^{3, 4} placed in very shallow water⁴ or on a floating mat of aquatic vegetation³ over water more than 50 cm deep¹. The nest may also be a shallow scrape⁴ on the ground amongst marsh vegetation⁴. The species breeds in small colonies and may forage up to 2-5 km from breeding sites¹. Management information In the Netherlands the provision of anchored artificial nesting rafts has been partly successful as a conservation measure^{7, 8}, especially in habitats where unstable nest substrates (such as floating water-lilies) result in poor breeding successes⁸. In the Netherlands there have also been successful programmes to reduce disturbance and improve habitat quality in agricultural areas, which has benefited the species⁷. The application of glyphosphate-based herbicides to combat and prevent the overgrowth of Typha spp. in wetlands may also benefit the species¹¹.

Threats On its breeding grounds the species is threatened by reductions in food availability due to the eutrophication of surface waters (which reduces the diversity of large insects)¹⁰, the acidification of lakes (which leads to the death of fish)¹⁰, the introduction of exotic fish species (e.g. peacock bass Cichla ocellaris)¹ and pesticide pollution (which may also lead to direct mortality from poisoning)¹. When breeding the species is also threatened by fluctuating water levels⁴, the loss and deterioration of freshwater nesting habitats^{1, 7} (e.g. through drainage for agriculture^{1, 4} and overgrowth of Typha spp. beds¹, 11), and human disturbance^{1, 4, 7} (especially where this forces breeding pairs to leave the nest before the young are fully fledged)⁹. The species is also susceptible to avian influenza so may be threatened by future outbreaks of the virus⁶.

References 1. del Hoyo et al. (1996). 2. Richards (1990). 3. Flint et al. (1984). 4. Snow and Perrins (1998). 5. Urban et al. (1986). 6. Melville and Shortridge (2006). 7. van der Winden (2005). 8. van der Winden et al. (2004). 9. van der winden (2002). 10. Beintema (1997). 11. Linz and Blixt (1997).

Further web sources of information

Detailed species account from Birds in Europe: population estimates, trends and conservation status (BirdLife International 2004)

Text account compilers Stuart Butchart (BirdLife International), Jonathan Ekstrom (BirdLife International), Lucy Malpas (BirdLife International)

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International)

Recommended citation BirdLife International (2010) Species factsheet: Chlidonias niger. Downloaded from http://www.birdlife.org on 6/9/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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